In Canada, the recovery of copper, nickel, lead and zinc from their ores produces over twelve million tons of slag per year. Since about 1900, some slags have been used for rail ballast, but usually large slag heaps have accumulated near the smelters. In recent years, at various mines in Europe and Australia, some smelter slags (usually copper smelter slags) have been ground to about -250 mesh and mixed with regular Portland cement to produce a blended cement for use in cemented mine backfill.
During the 1980's the pozzolanic (i.e. cementing) properties of Canadian smelter slags were studied to evaluate the feasibility of their use as a partial replacement for regular Portland cement and mine backfill. It was concluded that these slags could be so used. However, the results were much inferior to those obtained with regular Portland cement. For example, steel blast furnace slag mixtures only provided approximately 70% of the strength obtained by use of regular Portland cement or regular Portland cement/steel blast furnace slag mixtures. Consequently the work was discontinued, it also having been found that the economics, including transportation costs, were not favourable.
It has recently been found that large slap heaps are leaching unacceptably high amounts of heavy metal values, and mining companies are seeking acceptable solutions to this ground problem. Also, environmental authorities are requiring that plans be formulated for long term permanent solutions.
It is therefore an object of this invention to provide a method of using base metals smelter slag to produce a cement for general construction purposes, including mine backfill, whose properties will be equal to or better than those of regular Portland cement or regular Portland cement/blast furnace slag mixtures.